Wireless networks are first and foremost constrained by the limited resources of wireless spectrum. Different techniques are employed to allow coexistence of different wireless networks and simultaneous use of resources by multiple mobile terminals. Among such techniques, Time Division Multiple Access divides the use of a single wireless frequency into time slices; Frequency Division Multiple Access bases on using multiple non-overlapping frequency bands at the same time; with Code Division Multiple Access mobile stations use a wide frequency band simultaneously and separate the communication channels by using different pseudo codes.
Increased bandwidth demands and quality-of-service (QoS) requirements of the end-users present a challenge for the wireless network operators, which can be resolved only by increasing the base station density, limiting their range and thus allowing better and denser frequency reuse.
With increased base station density, the maintenance costs become prohibitive and such dense network maintenance and operation must become highly automated in order for the network to remain economically viable. The present invention relates to such automated base station frequency assignment with the aim of optimizing the throughput of the network per unit of area.
Different solutions relating to automated base station frequency selection exist. U.S. Pat. No. 6,253,086 B1 proposes adaptive frequency selection based on spectrum scans and the identification of a frequency that has the smallest transmission power or Received Signal Strength Indication (RSSI) at the location of the measuring base station. A similar approach is described in U.S. Pat. No. 5,212,831.
An important drawback of the presented methods is the problem of a hidden base station, where two base stations do not see each other and thus determine through signal strength measurements that a frequency is available and as such both choose the same frequency. At the location, from which both base stations are visible, the signals from both base stations can cause significant interference. U.S. Pat. No. 6,253,086 addresses the problem of the hidden base station by adaptive network planning using probes or mobile stations for signal strength (RSSI) measurements. U.S. Pat. No. 5,737,705 introduces an approach to solving additional problems, such as multiple base stations performing passive measurements simultaneously, possibly resulting in a multitude of stations selecting the same frequency at the same time.
All referenced inventions rely on RSSI measurements, either at the location of the base station or at the distributed locations using mobile stations. An important drawback of the described methods is the disregard of the estimated throughput provided by a base station and the surface area size, served by the said base station. A single base station, serving a surface area of one unit with sufficiently high RSSI to provide 100% relative throughput has ten times the throughput per surface area as a different base station which serves ten units of surface area with the same RSSI, providing 100% throughput. The former base station can thus serve respectively larger number of users or serve the same number of users with respectively larger throughputs.
In the preferred embodiment, this invention describes a method for automated frequency assignment on the basis of throughput per unit of area, hereafter referred to as AreaT. The method is based on an iterative simulation approach, wherein the centralized self-organizing network server performs calculations using the real-world measurements information about existing network and its base stations, combined with the nominal specifications (antenna diagram, output power), location and the direction of the newly installed base station.